1. Field
One embodiment of the present invention relates to a stamper to be used in the manufacture of a magnetic recording medium having discrete tracks on the surface of a magnetic recording layer and, more particularly, to a light-transmitting stamper for transferring three-dimensional patterns corresponding to discrete tracks onto a resist.
2. Description of the Related Art
Recently, a discrete track recording medium (DTR medium) having physically separated recording tracks has been proposed in order to increase the recording density of a magnetic recording medium.
In the process of manufacturing this DTR medium, as disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2003-157520, an imprinting stamper is pressed against a resist applied on the surface of a magnetic recording layer to transfer three-dimensional patterns onto the resist, and the magnetic recording layer is processed by using the resist as a mask.
Conventionally, an Ni stamper, father stamper, mother stamper, or son stamper formed by an electroforming process has been used as the imprinting stamper as described above. However, a long formation time of about 1 hr is required for one Ni stamper when the electroforming process is used, and the Ni stamper is unsuited to mass-production because the life of the Ni stamper is short. By contrast, when an initial Ni stamper is formed as a father stamper by the electroforming process and a mother stamper or son stamper is formed by using an injection molding process after that, one resin stamper is obtained for a short formation time of about a few sec.
The injection molding process as described above has been used in the manufacture of an optical disc.
For example, in an optical disc such as a DVD (Digital Versatile Disc) obtained by bonding two molded substrates, three-dimensional patterns having a track pitch of 300 nm or more are formed on at least one molded substrate, and an optical recording layer including the three-dimensional structure and having a thickness of 30 μm or more is formed.
In the DTR medium, however, patterns having a track pitch of 100 nm or less and a three-dimensional pattern height of 100 nm or less are formed. When the density of data is increased and the tracks are thus micropatterned, the life of the resin stamper readily shortens owing to the transfer and peeling of the resist patterns.
Also, when using a general defect testing apparatus, defects are normally detected by using the reflection of light. Unfortunately, a light-transmitting stamper such as the resin stamper has a low reflectance because the stamper transmits light. In addition, a defect test on the pattern upper surface is difficult to conduct because light from not only the pattern upper surface but also the pattern lower surface is reflected.